CompositeStorage: new Storage implementation

This is the backend for the upcoming "mount" command.

Makefile.am

@@ -428,6 +428,7 @@ libstorage_a_SOURCES = \
 	src/storage/StoragePlugin.hxx \
 	src/storage/Registry.cxx src/storage/Registry.hxx \
 	src/storage/StorageInterface.cxx src/storage/StorageInterface.hxx \
+	src/storage/CompositeStorage.cxx src/storage/CompositeStorage.hxx \
 	src/storage/Configured.cxx src/storage/Configured.hxx \
 	src/storage/plugins/LocalStorage.cxx src/storage/plugins/LocalStorage.hxx \
 	src/storage/FileInfo.hxx

src/storage/CompositeStorage.cxx

@@ -0,0 +1,344 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#include "config.h"
+#include "CompositeStorage.hxx"
+#include "FileInfo.hxx"
+#include "util/Error.hxx"
+#include "util/Domain.hxx"
+
+#include <set>
+
+static constexpr Domain composite_domain("composite");
+
+/**
+ * Combines the directory entries of another #StorageDirectoryReader
+ * instance and the virtual directory entries.
+ */
+class CompositeDirectoryReader final : public StorageDirectoryReader {
+	StorageDirectoryReader *other;
+
+	std::set<std::string> names;
+	std::set<std::string>::const_iterator current, next;
+
+public:
+	template<typename M>
+	CompositeDirectoryReader(StorageDirectoryReader *_other,
+				 const M &map)
+		:other(_other) {
+		for (const auto &i : map)
+			names.insert(i.first);
+		next = names.begin();
+	}
+
+	virtual ~CompositeDirectoryReader() {
+		delete other;
+	}
+
+	/* virtual methods from class StorageDirectoryReader */
+	virtual const char *Read() override;
+	virtual bool GetInfo(bool follow, FileInfo &info,
+			     Error &error) override;
+};
+
+const char *
+CompositeDirectoryReader::Read()
+{
+	if (other != nullptr) {
+		const char *name = other->Read();
+		if (name != nullptr) {
+			names.erase(name);
+			return name;
+		}
+
+		delete other;
+		other = nullptr;
+	}
+
+	if (next == names.end())
+		return nullptr;
+
+	current = next++;
+	return current->c_str();
+}
+
+bool
+CompositeDirectoryReader::GetInfo(bool follow, FileInfo &info,
+				  Error &error)
+{
+	if (other != nullptr)
+		return other->GetInfo(follow, info, error);
+
+	assert(current != names.end());
+
+	info.type = FileInfo::Type::DIRECTORY;
+	info.mtime = 0;
+	info.device = 0;
+	info.inode = 0;
+	return true;
+}
+
+static std::string
+NextSegment(const char *&uri_r)
+{
+	const char *uri = uri_r;
+	const char *slash = strchr(uri, '/');
+	if (slash == nullptr) {
+		uri_r += strlen(uri);
+		return std::string(uri);
+	} else {
+		uri_r = slash + 1;
+		return std::string(uri, slash);
+	}
+}
+
+CompositeStorage::Directory::~Directory()
+{
+	delete storage;
+}
+
+const CompositeStorage::Directory *
+CompositeStorage::Directory::Find(const char *uri) const
+{
+	const Directory *directory = this;
+	while (*uri != 0) {
+		const std::string name = NextSegment(uri);
+		auto i = directory->children.find(name);
+		if (i == directory->children.end())
+			return nullptr;
+
+		directory = &i->second;
+	}
+
+	return directory;
+}
+
+CompositeStorage::Directory &
+CompositeStorage::Directory::Make(const char *uri)
+{
+	Directory *directory = this;
+	while (*uri != 0) {
+		const std::string name = NextSegment(uri);
+#if defined(__clang__) || GCC_CHECK_VERSION(4,8)
+		auto i = directory->children.emplace(std::move(name),
+						     Directory());
+#else
+		auto i = directory->children.insert(std::make_pair(std::move(name),
+								   Directory()));
+#endif
+		directory = &i.first->second;
+	}
+
+	return *directory;
+}
+
+bool
+CompositeStorage::Directory::Unmount()
+{
+	if (storage == nullptr)
+		return false;
+
+	delete storage;
+	storage = nullptr;
+	return true;
+}
+
+bool
+CompositeStorage::Directory::Unmount(const char *uri)
+{
+	const std::string name = NextSegment(uri);
+
+	auto i = children.find(name);
+	if (i == children.end() || !i->second.Unmount())
+		return false;
+
+	if (i->second.IsEmpty())
+		children.erase(i);
+
+	return true;
+
+}
+
+bool
+CompositeStorage::Directory::MapToRelativeUTF8(std::string &buffer,
+					       const char *uri) const
+{
+	if (storage != nullptr) {
+		const char *result = storage->MapToRelativeUTF8(uri);
+		if (result != nullptr) {
+			buffer = result;
+			return true;
+		}
+	}
+
+	for (const auto &i : children) {
+		if (i.second.MapToRelativeUTF8(buffer, uri)) {
+			buffer.insert(buffer.begin(), '/');
+			buffer.insert(buffer.begin(),
+				      i.first.begin(), i.first.end());
+			return true;
+		}
+	}
+
+	return false;
+}
+
+CompositeStorage::CompositeStorage()
+{
+}
+
+CompositeStorage::~CompositeStorage()
+{
+}
+
+void
+CompositeStorage::Mount(const char *uri, Storage *storage)
+{
+	const ScopeLock protect(mutex);
+
+	Directory &directory = root.Make(uri);
+	if (directory.storage != nullptr)
+		delete directory.storage;
+	directory.storage = storage;
+}
+
+bool
+CompositeStorage::Unmount(const char *uri)
+{
+	const ScopeLock protect(mutex);
+
+	return root.Unmount(uri);
+}
+
+CompositeStorage::FindResult
+CompositeStorage::FindStorage(const char *uri) const
+{
+	FindResult result{&root, uri};
+
+	const Directory *directory = &root;
+	while (*uri != 0) {
+		const std::string name = NextSegment(uri);
+
+		auto i = directory->children.find(name);
+		if (i == directory->children.end())
+			break;
+
+		directory = &i->second;
+		if (directory->storage != nullptr)
+			result = FindResult{directory, uri};
+	}
+
+	return result;
+}
+
+CompositeStorage::FindResult
+CompositeStorage::FindStorage(const char *uri, Error &error) const
+{
+	auto result = FindStorage(uri);
+	if (result.directory == nullptr)
+		error.Set(composite_domain, "No such directory");
+	return result;
+}
+
+bool
+CompositeStorage::GetInfo(const char *uri, bool follow, FileInfo &info,
+			  Error &error)
+{
+	const ScopeLock protect(mutex);
+
+	auto f = FindStorage(uri, error);
+	if (f.directory->storage != nullptr &&
+	    f.directory->storage->GetInfo(f.uri, follow, info, error))
+		return true;
+
+	const Directory *directory = f.directory->Find(f.uri);
+	if (directory != nullptr) {
+		error.Clear();
+		info.type = FileInfo::Type::DIRECTORY;
+		info.mtime = 0;
+		info.device = 0;
+		info.inode = 0;
+		return true;
+	}
+
+	return false;
+}
+
+StorageDirectoryReader *
+CompositeStorage::OpenDirectory(const char *uri,
+				Error &error)
+{
+	const ScopeLock protect(mutex);
+
+	auto f = FindStorage(uri, error);
+	const Directory *directory = f.directory->Find(f.uri);
+	if (directory == nullptr || directory->children.empty()) {
+		/* no virtual directories here */
+
+		if (f.directory->storage == nullptr)
+			return nullptr;
+
+		return f.directory->storage->OpenDirectory(f.uri, error);
+	}
+
+	StorageDirectoryReader *other =
+		f.directory->storage->OpenDirectory(f.uri, IgnoreError());
+	return new CompositeDirectoryReader(other, directory->children);
+}
+
+std::string
+CompositeStorage::MapUTF8(const char *uri) const
+{
+	const ScopeLock protect(mutex);
+
+	auto f = FindStorage(uri);
+	if (f.directory->storage == nullptr)
+		return std::string();
+
+	return f.directory->storage->MapUTF8(f.uri);
+}
+
+AllocatedPath
+CompositeStorage::MapFS(const char *uri) const
+{
+	const ScopeLock protect(mutex);
+
+	auto f = FindStorage(uri);
+	if (f.directory->storage == nullptr)
+		return AllocatedPath::Null();
+
+	return f.directory->storage->MapFS(f.uri);
+}
+
+const char *
+CompositeStorage::MapToRelativeUTF8(const char *uri) const
+{
+	const ScopeLock protect(mutex);
+
+	if (root.storage != nullptr) {
+		const char *result = root.storage->MapToRelativeUTF8(uri);
+		if (result != nullptr)
+			return result;
+	}
+
+	if (!root.MapToRelativeUTF8(relative_buffer, uri))
+		return nullptr;
+
+	return relative_buffer.c_str();
+}

src/storage/CompositeStorage.hxx

@@ -0,0 +1,123 @@
+/*
+ * Copyright (C) 2003-2014 The Music Player Daemon Project
+ * http://www.musicpd.org
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License as published by
+ * the Free Software Foundation; either version 2 of the License, or
+ * (at your option) any later version.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License along
+ * with this program; if not, write to the Free Software Foundation, Inc.,
+ * 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA.
+ */
+
+#ifndef MPD_COMPOSITE_STORAGE_HXX
+#define MPD_COMPOSITE_STORAGE_HXX
+
+#include "check.h"
+#include "StorageInterface.hxx"
+#include "thread/Mutex.hxx"
+#include "Compiler.h"
+
+#include <string>
+#include <map>
+
+class Error;
+class Storage;
+
+/**
+ * A #Storage implementation that combines multiple other #Storage
+ * instances in one virtual tree.  It is used to "mount" new #Storage
+ * instances into the storage tree.
+ *
+ * This class is thread-safe: mounts may be added and removed at any
+ * time in any thread.
+ */
+class CompositeStorage final : public Storage {
+	/**
+	 * A node in the virtual directory tree.
+	 */
+	struct Directory {
+		/**
+		 * The #Storage mounted n this virtual directory.  All
+		 * "leaf" Directory instances must have a #Storage.
+		 * Other Directory instances may have one, and child
+		 * mounts will be "mixed" in.
+		 */
+		Storage *storage;
+
+		std::map<std::string, Directory> children;
+
+		Directory():storage(nullptr) {}
+		~Directory();
+
+		gcc_pure
+		bool IsEmpty() const {
+			return storage == nullptr && children.empty();
+		}
+
+		gcc_pure
+		const Directory *Find(const char *uri) const;
+
+		Directory &Make(const char *uri);
+
+		bool Unmount();
+		bool Unmount(const char *uri);
+
+		gcc_pure
+		bool MapToRelativeUTF8(std::string &buffer,
+				       const char *uri) const;
+	};
+
+	struct FindResult {
+		const Directory *directory;
+		const char *uri;
+	};
+
+	/**
+	 * Protects the virtual #Directory tree.
+	 *
+	 * TODO: use readers-writer lock
+	 */
+	mutable Mutex mutex;
+
+	Directory root;
+
+	mutable std::string relative_buffer;
+
+public:
+	CompositeStorage();
+	virtual ~CompositeStorage();
+
+	void Mount(const char *uri, Storage *storage);
+	bool Unmount(const char *uri);
+
+	/* virtual methods from class Storage */
+	virtual bool GetInfo(const char *uri, bool follow, FileInfo &info,
+			     Error &error) override;
+
+	virtual StorageDirectoryReader *OpenDirectory(const char *uri,
+						      Error &error) override;
+
+	virtual std::string MapUTF8(const char *uri) const override;
+
+	virtual AllocatedPath MapFS(const char *uri) const override;
+
+	virtual const char *MapToRelativeUTF8(const char *uri) const override;
+
+private:
+	gcc_pure
+	FindResult FindStorage(const char *uri) const;
+	FindResult FindStorage(const char *uri, Error &error) const;
+
+	const char *MapToRelativeUTF8(const Directory &directory,
+				      const char *uri) const;
+};
+
+#endif